1. Field of the Invention
This invention relates to a method of forming a multilayered structure and more particularly to a surface flattening technique for forming a multilayered structure.
This invention is applicable, for example, to a multilayered structure for multilayered wiring in a semiconductor integrated circuit, an optical integrated circuit, etc.
2. Related Background Art
Rapid advances in an integrated circuit technique have more and more reduced the size of components, in connection with which the multilayering of various components and wiring has advanced. For example, two-layer Al wiring is used by memory elements of 256K bits, and such wiring will tend to be multilayered in the future.
A problem with a multilayered structure is unevenness of the surface of a device due to wiring, etc., on the respective layers. Large unevenness may cause disconnection and reduce the yield and reliability the elements. Therefore, a technique for flattening an uneven surface is essential.
One conventional flattening technique is to form a glass layer of SiO.sub.2 and added phosphorus or boron an uneven surface, by CVD or coating, and flatten the resulting surface using a flow of glass due to heat. Since this method involves high-temperature processing, however, materials used for wiring, etc., are limited in kind.
Other flattening techniques have the problems that they make the steps complicated and increase the number of steps.